Automated control of a vehicle is well known and useful in a variety of applications. In the field of farming, tractors are often configured to travel on preset paths in order to efficiently cover an area. In the field of construction and road work, equipment is often controlled by an autonomous system to ensure the accuracy of vehicle paths, such as that of pavers and bulldozers. More recently, autonomous driving systems have been developed for passenger and freight vehicles on roadways.
Automated vehicles are controlled by a variety of means. Many are controlled with the aid of navigational satellite systems such as GPS. Such vehicles carry a GPS receiver to calculate the position of the vehicle by measuring the distance between itself and at least three GPS satellites. The position of the vehicle is determined by measuring the time delay between transmission and reception of a signal from each GPS satellite and triangulating the position of the vehicle based on this data. Other systems known in the art function by traveling over a preset path, garnering path data while doing so, and providing the data to a system for controlling a vehicle so that the vehicle can use the data to determine a path of travel. Similarly, map data may be provided to aid in controlling a vehicle.
Another method of automated control of a vehicle is dead reckoning navigation. In this method, vehicle position data is determined by calculating traveling distance as a function of the speed of the vehicle and an azimuth of the vehicle is estimated by using a gyroscope and an earth magnetism sensor, thereby estimating the position of the vehicle. This is often combined with an inertial navigation system whereby the position and the azimuth of the vehicle are estimated by using a gyroscope and measuring acceleration.
These and other such systems have the advantage of increased precision and decreased effort upon the part of a user, but such systems also come with drawbacks. Automated systems are known to malfunction and in a moving vehicle safety is essential. If a vehicle controlled by an automated system leaves the desired path, fertilizer may be placed over the wrong crops, the vehicle may turn over, or the vehicle may crash into an object such as a building. Without precise operation, there is a risk of destruction of property, loss of time and injury.
To compensate for these and other drawbacks of automated vehicles, systems have been developed whereby a vehicle reverts to manual control upon detection of an emergency or alarm state. Systems may also slow the speed of the vehicle while reverting to manual control. Further, systems known in the art may passively or actively return the steering wheel to a center position upon release of automated control.
U.S. Pat. No. 6,067,782 discloses an automated steering system for machines. In this system, movement of the steering wheel beyond a threshold value deactivates the automatic steering mode and switches to manual steering mode. U.S. Pat. No. 6,198,992 discloses overriding a guidance control system to disengage automatic steering when movement of a steering wheel is sufficiently abrupt. U.S. Pat. No. 6,751,535 discloses controlling an unmanned vehicle utilizing GPS, where upon losing the road position data, the vehicle is slowed to a stop.